The manufacture of mineral fiber thermal insulation is carried out according to one of a number of continuous processes wherein the molten mineral material flowing from a melting furnace is divided into streams and attenuated into fibers. The attenuation is effected by centrifuging and/or fluid jets to form discontinuous fibers of relatively small dimension which are collected by randomly depositing on a moving foraminous conveyor belt. The fibers are collected in a felted haphazard manner to form a mat. The volume of fiber in the mat will be determined by the speed of fiber formation and the speed of the belt. In order to produce most thermal insulating products, the fibers must be bonded together in an integral structure. To achieve this binding, a curable binder material is added to the mineral wool. The curable binder composition is generally formulated as a liquid to be sprayed onto the fibers as they are dropping onto the collecting conveyor belt. The layer of fiber with binder is then compressed and shaped into the form and dimensions of the desired thermal insulating product such as pipe or board and passed through a curing oven where the binder is cured fixing the size and shape of the finished insulating product by bonding the mass of fibers one to another forming an integral composite structure. Various materials have been used as binder ingredients including both organic and inorganic materials generally blended for different properties. The organic binder materials most commonly employed are heat curable thermosetting resin systems of the phenol formaldehyde type.
Such binders are generally provided as water soluble or water dispersable compositions which can be easily blended with other ingredients and diluted to low concentrations which are readily sprayed onto the fiber as it falls onto the collecting conveyor. The binder composition is generally applied in an amount such that the cured binder constitutes about 5% to about 10% by wt. of the finished product though it can be as little as 1% or less or as high as 20% or more, depending upon the type of fiber product. Optimally, the amount of binder for most thermal insulating products will be the amount necessary to lock each fiber into the mass by bonding the fibers where they cross or overlap. For this reason, it is desired to have binder compositions with good flow characteristics so that the binder solution can be applied to the fiber at a low volume that will flow to the fiber intersections.
Generally, the binder system requirements are for a low cost water soluble or water dispersable composition which can be easily applied and readily cured during normal production cycles. The product should be relatively stable for periods of time long enough to permit mixing and application at temperatures ordinarily encountered in fiberizing plants and the composition should be dilutable in order to permit variations in concentrations for different end products. The cured binder product must provide a strong bond with sufficient elasticity and thickness recovery to permit reasonable shipping and in-service deformation of the thermal insulating product. It must be moisture resistant so that is will not swell under humid conditions. It must be odor free and non-corrosive to metals with which it comes in contact. The binder should be capable of withstanding temperatures as high as the temperature that the mineral fiber can withstand, particularly for pipe insulation where the pipeline is used for hot fluids. The mineral fibers can be any of the materials which are capable of being fiberized. Typical binder compositions for glass are prepared as aqueous solutions or dispersions of partially condensed phenolic formaldehyde resins to which are added a variety of modifiers or agents to improve the spraying, flowing or similar application characteristics as well as the bonding strength, temperature resistence and other in-service features of the cured resin.
A binder composition much desired is one that can withstand service temperatures of 700.degree. to 950.degree. F. Numerous attempts have been made to provide such high temperature resistant binders with little acceptance for practical commercial utility. A particularly troublesome aspect of binders prepared from phenol formaldehyde resin systems is the tendency towards punking when subjected to temperatures in excess of 600.degree. F. and higher which are within the range of temperatures that may be encountered in use. The phenol formaldehyde resin system in the final thermoset stages can undergo exothermic oxidation. Since the mineral fiber product is an excellent heat insulator, the heat given off by any exothermic reaction in the binder is confined and becomes cummulative until temperatures are attained which cause thermal decomposition of the organic binder materials. In some instances, the decomposition products will have an ignition temperature lower than the corresponding temperature of the surrounding composition and may burst into flame.
The characteristic of exothermic decomposition without flame is referred to as "punking". It can continue at a slow rate for a considerable length of time ultimately resulting in total decomposition of the binder with consequent deterioration of the fiberglass insulating product. Punking can be initiated in the cured phenolic binder systems by subjecting the thermal insulating product to elevated temperatures. There are very few mineral fiber thermal insulations produced with phenolic resin compositions that are commercially available at the present time which can withstand temperatures in excess of about 600.degree. F. to 700.degree. F. without punking though numerous attempts have been made to formulate suitable binder compositions which can withstand high temperatures since generally the glass fibers can withstand temperatures up to 1200.degree. to 1300.degree. F. before softening. In fact, the glass fiber most commonly used in thermal insulating products at present has a Littleton softening point between 1250.degree. and 1300.degree. F. Accordingly, there is a definite need for a high temperature resistant binder which will extend the use of these glass fiber materials to high temperature service.
In the past, a variety of approaches have been taken in an effort to formulate high temperature binder compositions using phenolic resins as the primary binder ingredient. Modification of the phenolic formaldehyde by the addition of nitrogeneous modifiers such as dicyandiamide are disclosed in U.S. Pat. No. 3,223,668. Others have tried the use of borates of various sorts as additions to the binder composition; U.S. Pat. No. 2,931,738, U.S. Pat. No. 3,002,857, U.S. Pat. No. 3,253,948 and U.S. Pat. No. 3,839,236.
Where modified binder compositions have been employed to achieve high temperature resistence, frequently, the ingredients intended to improve anti-punking properties of the phenolic resin have also altered the curing property so that a complete cure is either not achievable or can be achieved only over a period of time which is not practical for normal production in manufacture of thermal insulating products. In still other cases, other properties such as dilutability, sprayability, bonding strength and the like have been adversely affected.
Thus among the many patents pertaining to binders, the problem of punking has been repeatedly addressed though the problem still exists and commercial products which employ a phenolic resin system and which can be used under circumstances where temperatures in excess of 600.degree. F. are encountered are presently uncommon. It is believed that the present novel binder composition fills the recognized need for a phenolic binder system that has all of the necessary properties and which will cure to provide a binder that can withstand temperatures in the range of 700.degree. to 950.degree. F.
In approaching the problem in formulating binder compositions with phenolics, it is recognized that the chemical composition cannot be precisely established in view of the recognized uncertainty with respect to the composition of phenolic formaldehyde condensations. Furthermore, since it is desired to use low cost material in formulating binder compositions, the phenolic starting materials generally employed are not of high purity so that the condensates are formed from a phenol which is itself a mixture of materials. In order to achieve desired reproduceability with phenolic binder compositions, efforts are often directed towards reproducing the functional characteristics by on-line adjustment since it is preferred to have consistent performance characteristics. Accordingly, consistent binder compositions can be produced by measuring the product quality and adjusting the composition to provide consistent quality even though the composition of the binder system may vary owing to variations in the starting materials and the adjustments in blending with other ingredients. Checking the end product in order to determine the proportion of ingredients or the reaction conditions for preparing phenol formaldehyde resin systems has been done in the past, for example, in U.S. Pat. No. 3,248,368, the phenol formaldehyde condensation process is controlled to produce desired end results. Other approaches have been to blend various condensation products, for example as taught by U.S. Pat. No. 3,207,652.
Accordingly, it is possible to provide a binder composition which can be formulated continuously or if batchwise then batches of consistent quality can be produced by monitoring the characteristics of the cured binder and altering the composition to provide consistent performance characteristics such as temperature resistance, bonding strength, sprayability and the like. To this end, the present invention sets forth several specific formulations for new high temperature binder compositions and further it teaches a method of preparing binder compositions and thermal insulation products in which the ingredients are combined in accordance with stoichiometric proportions determined by the nature of the phenol formaldehyde starting material. Stoichiometric control is achieved through titration to determine the necessary quantities and by thermal analysis of the end product. The novel binder compositions can be employed in thermal insulation manufacturing operations currently in use commercially, to provide a product with consistent and reliable high temperature resistance, good sprayability and flow characteristics and high bonding strength and which will cure under process conditions generally in use in the production of glass fiber thermal insulation.
Accordingly, it is an object of the present invention to produce an inexpensive polymerizable aqueous phenolic binder composition which, when cured, will not exhibit any punking under continuous high temperature service within a range of 700.degree. to 950.degree. F.
These and other aspects of the invention will be more fully understood from the description and claims which follow. The description of the background for this invention as well as the disclosure of the improved binder products is made by reference to glass fiber products though it is to be understood that the disclosure applies equally to other mineral fiber products.